The Orange Revolution that brought Mr Yushchenko to power was fuelled partly by popular anger over the corruption of the previous government headed by President Leonid Kuchma.

Rivals: Petro Poroshenko and Yulia Tymoshenko

Weeks of mass demonstrations forced a re-run of the elections, which had been widely condemned as rigged.

Mr Yushchenko won the final vote and took office in January. A coalition government including ministers from his Our Ukraine party, the Yulia Tymoshenko Bloc and the Socialist Party, was formed the next month.

"Separate blocs that emerged within the team began playing their own games behind closed doors, which was rather unpleasant," Mr Yushchenko told journalists.

"This involved digging out compromising material, making photos, blackmail and so forth and so on."

He added: "Interpersonal conflicts have grown into conflicts between teams and begun affecting state affairs."